Method and system for controlling helicopter vibrations

ABSTRACT

A method/system for controlling helicopter vibrations is provided that includes a vibration canceling force generator for actively generating a vibration canceling force. The system includes a resonant actuator having a natural resonant frequency and a resonant actuator electronic control system. The resonant actuator electronic control system provides an electrical drive current to the resonant actuator to drive the resonant actuator about the resonant frequency when commanded by a received command signal. The resonant actuator has a feedback output with the feedback output fed back into the resonant actuator electronic control system wherein the resonant actuator electronic control system adjusts the electrical drive current based on the resonant actuator feedback output to generate the vibration canceling force.

CROSS REFERENCE

This application is a continuation of U.S. patent application Ser. No.11/149,514 filed Jun. 10, 2005, which claims the benefit of, andincorporates by reference Provisional Patent Application No. 60/578,645filed on Jun. 10, 2004.

FIELD OF THE INVENTION

The present invention relates to a method/system for controllingproblematic vibrations. More particularly the invention relates to amethod and system for controlling aircraft vehicle vibrations,particularly a method and system for canceling problematic rotary winghelicopter vibrations.

BACKGROUND OF THE INVENTION

Helicopter vibrations are particularly troublesome in that they cancause fatigue and wear on the equipment and occupants in the aircraft.In vehicles such as helicopters, vibrations are particularly problematicin that they can damage the actual structure and components that make upthe vehicle in addition to the contents of the vehicle.

There is a need for a system and method of accurately and economicallycanceling vehicle vibrations. There is a need for a system and method ofaccurately and economically controlling vibrations. There is a need foran economically feasible method of controlling vibrations in ahelicopter so that the vibrations are efficiently cancelled andminimized. There is a need for a robust system of controlling vibrationsin a helicopter so that the vibrations are efficiently cancelled andminimized. There is a need for an economic method/system for controllingproblematic helicopter vibrations.

SUMMARY OF THE INVENTION

The invention includes a vibration canceling force generator foractively generating a vibration canceling force. The vibration cancelingforce generator includes a resonant actuator having a natural resonantfrequency, and a resonant actuator electronic control system having acommand input for receiving a command signal with the resonant actuatorelectronic control system providing an electrical drive current to theresonant actuator to drive the resonant actuator about the resonantfrequency when commanded by a received command signal, and the resonantactuator has a feedback output with the feedback output fed back intothe resonant actuator electronic control system wherein the resonantactuator electronic control system adjusts the electrical drive currentbased on the resonant actuator feedback output to generate the vibrationcanceling force.

The invention includes a method of making a vibration canceling forcegenerator. The method includes providing a resonant actuator having anatural resonant frequency, providing a resonant actuator electroniccontrol system having a command input for receiving a command signal anda power amplifier for providing an electrical drive current to drive theresonant actuator, and connecting the resonant actuator with theresonant actuator electronic control system wherein the resonantactuator electronic control system electrical drive current drives theresonant actuator about the natural resonant frequency when commanded bya received command signal, with the resonant actuator feeding anelectrical output back into the resonant actuator electronic controlsystem wherein the resonant actuator electronic control system adjuststhe electrical drive current based on the resonant actuator electricaloutput.

The invention includes a method of controlling vibrations. The methodincludes providing a resonant actuator having a natural resonantfrequency, providing a resonant actuator electronic control system forproviding an electrical drive current to drive the resonant actuator,connecting the resonant actuator with the resonant actuator electroniccontrol system, and driving the resonant actuator about the naturalresonant frequency with the resonant actuator feeding an electricaloutput back into the resonant actuator electronic control system andadjusting the electrical drive current based on the resonant actuatorelectrical output.

The invention includes a vehicle vibration canceling system. The vehiclevibration canceling system includes a resonant actuator having a naturalresonant frequency. The vehicle vibration canceling system includes aresonant actuator electronic controller for providing an electricaldrive current to the resonant actuator to drive the resonant actuatorabout the resonant frequency. The resonant actuator has a feedbackelectrical output with the feedback electrical output fed back into theresonant actuator electronic controller wherein said resonant actuatorelectronic controller adjusts said electrical drive current based onsaid resonant actuator feedback electrical output.

The invention includes a method of making a helicopter vibrationcanceling system. The method includes providing a resonant actuatorhaving a natural resonant frequency. The method includes providing aresonant actuator electronic control system for providing an electricaldrive current to drive said resonant actuator. The method includesconnecting the resonant actuator with the resonant actuator electroniccontrol system wherein the resonant actuator electronic control systemelectrical drive current drives the resonant actuator about the naturalresonant frequency with said resonant actuator feeding an electricaloutput back into the resonant actuator electronic control system whereinthe resonant actuator electronic control system adjusts the electricaldrive current based on the resonant actuator electrical output.

The invention includes a method of controlling helicopter vibrations.The method includes providing a resonant actuator having a naturalresonant frequency. The method includes mounting the resonant actuatorin a helicopter. The method includes providing a resonant actuatorelectronic control system for providing an electrical drive current todrive the resonant actuator. The method includes connecting the resonantactuator with the resonant actuator electronic control system. Themethod includes driving the resonant actuator about the natural resonantfrequency with the resonant actuator feeding an electrical output backinto the resonant actuator electronic control system and adjusting theelectrical drive current based on the resonant actuator electricaloutput.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary of the invention, andare intended to provide an overview or framework for understanding thenature and character of the invention as it is claimed. The accompanyingdrawings are included to provide a further understanding of theinvention, and are incorporated in and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprincipals and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows methods and systems for controlling vibrations.

FIG. 2A-D show resonant actuators for controlling vibrations.

FIG. 3 shows methods and systems for controlling vibrations.

FIG. 4A-B show methods and systems for controlling vibrations.

FIG. 5 shows methods and systems for controlling vibrations.

FIG. 6 shows methods and systems for controlling vibrations.

FIG. 7 shows methods and systems for controlling vibrations.

FIG. 8 is a plot of Force (N) y-axis and Frequency (Hz) x-axis (ActuatorForce for 0.75 volt command).

FIG. 9 is a plot of Actuator Current (amps) y-axis and Frequency (Hz)x-axis (Actuator Current for 0.75 volt command).

FIG. 10 is a plot of Actuator Voltage (volts) y-axis and Frequency (Hz)x-axis (Actuator Voltage for 0.75 volt command).

FIG. 11 is a plot of Actuator Power (watts) y-axis and Frequency (Hz)x-axis (Actuator Power for 0.75 volt command).

FIG. 12 is a plot of Resistive Power (watts) y-axis and Frequency (Hz)x-axis (Actuator Power for 0.75 volt command).

FIG. 13 is a plot of Actuator Mass Displacement (mm) y-axis and Time (s)x-axis (Actuator Response to Step Input of 0.75 Volts).

FIG. 14 is a plot of Actuator Mass Displacement (mm) y-axis and Time (s)x-axis (Actuator Response to 0.75 Volts Command at 22.1 Hz).

FIG. 15 is a plot of Force (N) y-axis and Frequency (Hz) x-axis(Actuator Force for 0.75 volt command).

FIG. 16 is a plot of Actuator Current (amps) y-axis and Frequency (Hz)x-axis (Actuator Current for 0.75 volt command).

FIG. 17 is a plot of Actuator Voltage (volts) y-axis and Frequency (Hz)x-axis (Actuator Voltage for 0.75 volt command).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

The invention comprises a vibration canceling force generator foractively generating a vibration canceling force. The vibration cancelingforce generator includes a resonant actuator having a natural resonantfrequency, and a resonant actuator electronic control system with theresonant actuator electronic control system providing an electricaldrive current to the resonant actuator to drive the resonant actuatorabout the resonant frequency when commanded. The resonant actuator has afeedback output with the feedback output fed back into the resonantactuator electronic control system wherein the resonant actuatorelectronic control system adjusts the electrical drive current based onthe resonant actuator feedback output to generate the vibrationcanceling force.

The invention includes a vibration canceling force generator foractively generating a vibration canceling force. The vibration cancelingforce generator includes a resonant actuator having a natural resonantfrequency, and a resonant actuator electronic control system having acommand input for receiving a command signal with the resonant actuatorelectronic control system providing an electrical drive current to theresonant actuator to drive the resonant actuator about the resonantfrequency when commanded by a received command signal, and the resonantactuator has a feedback output with the feedback output fed back intothe resonant actuator electronic control system wherein the resonantactuator electronic control system adjusts the electrical drive currentbased on the resonant actuator feedback output to generate the vibrationcanceling force. As shown in FIG. 1-5 the vibration canceling forcegenerator 20 actively generates a vibration canceling force 22 whichdestructively interferes with and cancels an unwanted vibration force ina structure 50 that it is attached to. The vibration canceling forcegenerator 20 preferably includes a linear voice coil resonant actuator24 having a natural resonant frequency 46. Preferably the resonantactuator 24 is an electromagnetically driven sprung mass 26 suspended onresilient metal flexures 32. As shown in FIG. 2A-D, the EM(ElectroMagnetic) driven mass 26 is preferably suspended on a horizontalbeam stack of multiple layers of resilient metal flexures 32, which arepreferably supported by two vertical side resilient metal flexures postplates, to provide a sprung mass that can be electromagnetically drivento oscillate at its natural resonant frequency. Preferably the resonantactuator sprung mass is driven by modulating an electromagnetic field sothe sprung mass is attracted and repelled by the EM field at itsresonant frequency. Preferably the resonant actuator sprung massincludes a permanent magnet 28 in alignment with an electromagnetic coil30, wherein a electrical drive current supplied to the EM coil 30 drivesthe sprung mass at resonance. The vibration canceling force generator 20includes a resonant actuator electronic control system 34. Preferablythe resonant actuator electronic control system 34 has a command input36 for receiving a command signal 38 and the resonant actuatorelectronic control system includes a power amplifier 40 that producesthe electrical drive current (i). The resonant actuator electroniccontrol system 34 provides an electrical drive current 42 to theresonant actuator 24 to drive the resonant actuator about the resonantfrequency when commanded by a received command signal 38, with theresonant actuator having a feedback output 44 fed back into the resonantactuator electronic control system wherein the resonant actuatorelectronic control system adjusts the electrical drive current (i) basedon the resonant actuator feedback output 44 to generate the vibrationcanceling force 22. Preferably the resonant actuator 24 has a resonantactuator natural resonant frequency in a range of 15 to 40 Hz, morepreferably in the range of 15-30 Hz, and most preferably in the range of18 to 26 Hz. The vibration canceling force generator 20 is able to adaptto an aging of the resonant actuator 24 that alters the resonantactuator natural resonant frequency changes over an extended operationlife time frame such as from the aging of the metal flexures andloosening of the metal flexure fasteners and fixtures over time,preferably with the utilization of the resonant actuator feedback output44 to adjust the drive current to the resonant actuators aging naturalresonant frequency so that the control system produced drive current canfollow an aging change in the natural frequency over an extended periodof time. Preferably the resonant actuator 24 has a damping level lessthan four percent of critical damping, more preferably a damping levelless than two percent of critical damping. Preferably the resonantactuator 24 is a lightly damped resonant actuator. Preferably theresonant actuator 24 is a lightly damped resonant actuator with aneffective damping ratio less than 0.5 (preferably with dampingratio=particular damping coefficient c/critical damping coefficientc_(r)). The vibration canceling force generator 20 utilizes a resonantactuator 24 that has a lightly damped mass spring system highly resonantresponse, with the actuator driven at resonance because of its highlyresonant response. Preferably the command signal 38 is an analog inputvoltage, which is received by command input 36 with the variable voltageinput command signal commanding the electronic control system 34 toproduce a force 22 to cancel the unwanted vibration force in thevibrating structure 50. As shown in FIG. 4, preferably the vibrationcanceling force generator includes electrical connector interfaces 52for disengagably connecting the resonant actuator 24 to the resonantactuator electronic control system 34. Such an electrical connectorinterface preferably includes a feedback loop connector 52 and anelectrical drive current connector 52, with the connector interfaces 52providing for interchanging of actuators 24 with the control systems 34and the replacement and swapping of resonant actuators 24. Preferablythe resonant actuator feedback output 44 is an electrical output fromthe resonant actuator back into the control system 34. In a preferredembodiment the actuator electrical output is directly fed from theactuator electrical output into the control system. In a preferredembodiment such as shown in FIG. 1, no separate physical actuator motionsensor for producing the feedback output is utilized, with theelectrical feedback output 44 coming directly from the actuator andcontrol system drive current. Preferably the resonant actuatorelectrical feedback output 44 is an electrical charge flow rate (i)through the resonant actuator, with the current (i_act) through theactuator fed back into the control system, with the actuator drivecurrent (i) controlled and limited to a maximum operation value.Preferably the control system uses the current (i_act) feedback 44 incontrolling the drive current (i) to drive the actuator at resonance andwithout the need of shape filtering. In an embodiment the resonantactuator feedback output 44 is an electrical potential differencethrough the resonant actuator 24, with the voltage (v_act) across theactuator fed back into the control system, with the voltage in theactuator controlled and limited to a maximum value corresponding to therated voltage for the actuator for maximum operation displacement of theactuator at resonance. In an embodiment the resonant actuator feedbackoutput 44 is the electrical charge flow rate (i_act) through theresonant actuator and the electrical potential difference (v_act)through the resonant actuator, with both the voltage and current fedback from actuator 24.

The invention comprises a method of making a vibration canceling forcegenerator. The method includes providing a resonant actuator having anatural resonant frequency, providing a resonant actuator electroniccontrol system having a power amplifier for providing an electricaldrive current to drive the resonant actuator, and connecting theresonant actuator with the resonant actuator electronic control systemwherein the resonant actuator electronic control system electrical drivecurrent drives the resonant actuator about the natural resonantfrequency when commanded by a received command signal, with the resonantactuator feeding an electrical output back into the resonant actuatorelectronic control system wherein the resonant actuator electroniccontrol system adjusts the electrical drive current based on theresonant actuator electrical output.

The invention includes a method of making a vibration canceling forcegenerator 20. The method includes providing a resonant actuator 24having a natural resonant frequency, providing a resonant actuatorelectronic control system 34 having a command input for receiving acommand signal and a power amplifier for providing an electrical drivecurrent (i) to drive the resonant actuator, and connecting the resonantactuator with the resonant actuator electronic control system whereinthe resonant actuator electronic control system electrical drive current(i) drives the resonant actuator about the natural resonant frequencywhen commanded by a received command signal, with the resonant actuatorfeeding an electrical output 44 back into the resonant actuatorelectronic control system wherein the resonant actuator electroniccontrol system adjusts the electrical drive current (i) based on theresonant actuator electrical output 44. Providing resonant actuator 24preferably includes providing an electromagnetically driven voice coil,preferably a sprung mass 26 driven by modulating a electromagnetic fieldproduced by an EM coil 30 so the sprung mass is attracted and repelledby the EM field and the actuator resonates at its natural resonantfrequency. Providing the resonant actuator electronic control system 34preferably includes providing a resonant actuator electronic controlsystem having a command input 36 for receiving a command signal 38 and apower amplifier 40 for providing an electrical drive current (i) todrive the resonant actuator about its resonant frequency. Preferably thecommand signal 38 is an analog input voltage, with the analog variablevoltage input command signal commanding the control system to produce avibration canceling force 22 which destructively interferes with andcancels an unwanted vibration force in the structure 50 that theactuator 24 is attached to. In a preferred embodiment such as shown inFIG. 1, the actuator electrical output 44 is fed back directly into thecontrol system, preferably with no separate physical actuator motionsensor needed for producing the feedback output. In an alternativeembodiment, such as shown in FIG. 4, the resonant actuator electricaloutput 44 includes an actuator sensor electrical output from an actuatorsensor 54. The actuator sensor 54 provides an actuator sensor electricaloutput 44 relative to a physical motion characteristic of the actuator24, such as a motion sensor measuring the motion of the moving mass 26.In an embodiment the actuator sensor 54 is an accelerometer mounted onthe actuator driven sprung mass. In an embodiment the actuator sensor 54is a velocity sensor measuring and sensing the velocity of the actuatordriven sprung mass. In an embodiment the actuator sensor 54 is adisplacement sensor measuring and sensing the displacement and positionof the actuator driven sprung mass. Providing the resonant actuator 24,preferably includes providing a resonant actuator with a naturalresonant frequency in the range of 15 to 40 Hz, more preferably 15-30Hz, and most preferably 18 to 26 Hz. Providing the resonant actuator 24,preferably includes providing a resonant actuator which has a dampinglevel less than four percent of critical damping, more preferably lessthan two percent of critical damping. Preferably the actuator 24 is alightly damped resonant actuator with an effective damping ratio lessthan 0.5 (damping ratio=particular damping coefficient c/criticaldamping coefficient c_(r)). Preferably the actuator 24 has the highlyresonant response of a lightly damped mass spring system. In anembodiment the method includes providing an electrical connectorinterface 52 for disengagably connecting the resonant actuator 24 to theresonant actuator electronic control system 34, preferably including afeedback output loop connectors 52, and electrical drive currentconnectors 52, with the disengagement and engagement of the connectorinterfaces used to interchange of actuators 24 with the control system34, and for replacing and swapping out actuators 24 driven by thecontrol system 34. Feeding back the electrical feedback 44 preferablyincludes feeding back the electrical charge flow rate through theresonant actuator. The current (i) through the actuator 24 is fed backinto the control system as (i_act) with the drive current controlled andlimited to a maximum operation value, most preferably with no shapefiltering used to drive the actuator 24. In an embodiment of theinvention feeding back the electrical feedback 44 preferably includesfeeding back the electrical potential difference through the resonantactuator. The voltage across the actuator fed back into the controlsystem as (v_act), with the voltage is controlled and limited to amaximum value corresponding to the rated voltage for the actuator 24 formaximum operation displacement of the actuator at resonance. In anembodiment feeding back the electrical feedback 44 preferably includesfeeding back both the electrical charge flow rate through the resonantactuator and the electrical potential difference through the resonantactuator, with both the voltage and current feedback from actuator.

The invention comprises a method of controlling vibrations. The methodincludes providing a resonant actuator having a natural resonantfrequency, providing a resonant actuator electronic control system forproviding an electrical drive current to drive the resonant actuator,connecting the resonant actuator with the resonant actuator electroniccontrol system, and driving the resonant actuator about the naturalresonant frequency with the resonant actuator feeding an electricaloutput back into the resonant actuator electronic control system andadjusting the electrical drive current based on the resonant actuatorelectrical output.

The invention includes a method of controlling vibrations. The methodincludes providing a voice coil resonant actuator 24 having a naturalresonant frequency, preferably an electromagnetically driven sprung massdriven by modulating a electromagnetic field so the sprung mass isattracted and repelled by the EM field. The method includes providing aresonant actuator electronic control system 34 for providing anelectrical drive current to drive the resonant actuator and connectingthe resonant actuator with the resonant actuator electronic controlsystem. The method includes driving the resonant actuator about thenatural resonant frequency with the resonant actuator feeding anelectrical output back into the resonant actuator electronic controlsystem and adjusting the electrical drive current based on the resonantactuator electrical output. Preferably providing a resonant actuator 24includes providing a resonant actuator with a natural resonant frequencyin a range of 15 to 40 Hz, more preferably 15-30 Hz, and most preferably18 to 26 Hz. Preferably providing a resonant actuator 24 includesproviding a resonant actuator with a damping level less than fourpercent of critical damping, more preferably less than two percent ofcritical damping. Preferably the lightly damped resonant actuator 24 hasan effective damping ratio less than 0.5 (damping ratio=particulardamping coefficient c/critical damping coefficient c_(r)), with theactuator having the highly resonant response of a lightly damped massspring system. Preferably the method includes providing an electricalconnector interface 52 for disengagably connecting the resonant actuatorto the resonant actuator electronic control system. Preferably theresonant actuator electrical output 44 is an electrical potentialdifference through the resonant actuator with the voltage across theactuator fed back into the control system, with voltagecontrolled/limited to a maximum value corresponding to the rated voltagefor the actuator for maximum operation displacement of the actuator atresonance. Preferably the resonant actuator electrical output 44 is anelectrical charge flow rate through the resonant actuator. Preferablythe resonant actuator electrical output is an electrical charge flowrate through the resonant actuator and an electrical potentialdifference through the resonant actuator. In an embodiment the resonantactuator electrical output is an actuator sensor electrical output.

The invention includes a vehicle vibration canceling system. The vehiclevibration canceling system includes a resonant actuator having a naturalresonant frequency. The vehicle vibration canceling system includes aresonant actuator electronic controller for providing an electricaldrive current to the resonant actuator to drive the resonant actuatorabout the resonant frequency. The resonant actuator has a feedbackelectrical output with the feedback electrical output fed back into theresonant actuator electronic controller wherein said resonant actuatorelectronic controller adjusts said electrical drive current based onsaid resonant actuator feedback electrical output.

The invention includes a vehicle vibration canceling system. Theaircraft vehicle vibration canceling system includes a resonant actuator24 having a natural resonant frequency, and a resonant actuatorelectronic controller 34, with the resonant actuator electroniccontroller providing an electrical drive current to the resonantactuator to drive the resonant actuator about the resonant frequency,with the resonant actuator having a feedback electrical output, thefeedback electrical output fed back into the resonant actuatorelectronic controller wherein the resonant actuator electroniccontroller adjusts the electrical drive current based on the resonantactuator feedback electrical output to produce a vibration canceling for22 to cancel a vibration in the vehicle vibrating structure 50 to whichit is attached. Preferably the resonant actuator 24 is anelectromagnetically driven sprung mass 26 suspended on resilient metalflexures 32. As shown in FIG. 2A-D, the EM driven mass 26 is preferablysuspended on a horizontal beam stack of multiple layers of resilientmetal flexures 32, which are preferably supported by two vertical sideresilient metal flexures post plates, to provide a sprung mass that canbe electromagnetically driven to oscillate at its natural resonantfrequency. Preferably the resonant actuator sprung mass is driven bymodulating an electromagnetic field so the sprung mass is attracted andrepelled by the EM field at its resonant frequency. Preferably theresonant actuator sprung mass includes a permanent magnet 28 inalignment with an electromagnetic coil 30, wherein a electrical drivecurrent supplied to the EM coil 30 drives the sprung mass at resonance.The vibration canceling force generator 20 includes a resonant actuatorelectronic control system 34. Preferably the resonant actuatorelectronic control system 34 has a command input 36 for receiving acommand signal 38 and the resonant actuator electronic control systemincludes a power amplifier 40 that produces the electrical drive current(i). The resonant actuator electronic control system 34 provides anelectrical drive current 42 to the resonant actuator 24 to drive theresonant actuator about the resonant frequency when commanded by areceived command signal 38, with the resonant actuator having a feedbackoutput 44 fed back into the resonant actuator electronic control systemwherein the resonant actuator electronic control system adjusts theelectrical drive current (i) based on the resonant actuator feedbackoutput 44 to generate the vibration canceling force 22. Preferably theresonant actuator 24 has a resonant actuator natural resonant frequencyin a range of 15 to 40 Hz, more preferably in the range of 15-30 Hz, andmost preferably in the range of 18 to 26 Hz. The vibration cancelingforce generator 20 is able to adapt to an aging of the resonant actuator24 that alters the resonant actuator natural resonant frequency changesover an extended operation life time frame such as from the aging of themetal flexures and loosening of the metal flexure fasteners and fixturesover time, preferably with the utilization of the resonant actuatorfeedback output 44 to adjust the drive current to the resonant actuatorsaging natural resonant frequency so that the control system produceddrive current can follow an aging change in the natural frequency overan extended period of time. Preferably the resonant actuator 24 has adamping level less than four percent of critical damping, morepreferably a damping level less than two percent of critical damping.Preferably the resonant actuator 24 is a lightly damped resonantactuator. Preferably the resonant actuator 24 is a lightly dampedresonant actuator with an effective damping ratio less than 0.5(preferably with damping ratio=particular damping coefficient c/criticaldamping coefficient c_(r)). The vibration canceling force generator 20utilizes a resonant actuator 24 that has a lightly damped mass springsystem highly resonant response, with the actuator driven at resonancebecause of its highly resonant response. Preferably the command signal38 is an analog input voltage, which is received by command input 36with the variable voltage input command signal commanding the electroniccontrol system 34 to produce a force 22 to cancel the unwanted vibrationforce in the vibrating structure 50. As shown in FIG. 4, preferably thevibration canceling force generator includes electrical connectorinterfaces 52 for disengagably connecting the resonant actuator 24 tothe resonant actuator electronic control system 34. Such an electricalconnector interface preferably includes a feedback loop connector 52 andan electrical drive current connector 52, with the connector interfaces52 providing for interchanging of actuators 24 with the control systems34 and the replacement and swapping of resonant actuators 24. Preferablythe resonant actuator feedback output 44 is an electrical output fromthe resonant actuator back into the control system 34. In a preferredembodiment the actuator electrical output is directly fed from theactuator electrical output into the control system. In a preferredembodiment such as shown in FIG. 1, no separate physical actuator motionsensor for producing the feedback output is utilized, with theelectrical feedback output 44 coming directly from the actuator andcontrol system drive current. Preferably the resonant actuatorelectrical feedback output 44 is an electrical charge flow rate (i)through the resonant actuator, with the current (i_act) through theactuator fed back into the control system, with the actuator drivecurrent (i) controlled and limited to a maximum operation value.Preferably the control system uses the current (i_act) feedback 44 incontrolling the drive current (i) to drive the actuator at resonance andwithout the need of shape filtering. In an embodiment the resonantactuator feedback output 44 is an electrical potential differencethrough the resonant actuator 24, with the voltage (v_act) across theactuator fed back into the control system, with the voltage in theactuator controlled and limited to a maximum value corresponding to therated voltage for the actuator for maximum operation displacement of theactuator at resonance. In an embodiment the resonant actuator feedbackoutput 44 is the electrical charge flow rate (i_act) through theresonant actuator and the electrical potential difference (v_act)through the resonant actuator, with both the voltage and current fedback from actuator 24.

The invention includes a method of making a helicopter vibrationcanceling system. The method includes providing a resonant actuatorhaving a natural resonant frequency. The method includes providing aresonant actuator electronic control system for providing an electricaldrive current to drive said resonant actuator. The method includesconnecting the resonant actuator with the resonant actuator electroniccontrol system wherein the resonant actuator electronic control systemelectrical drive current drives the resonant actuator about the naturalresonant frequency with said resonant actuator feeding an electricaloutput back into the resonant actuator electronic control system whereinthe resonant actuator electronic control system adjusts the electricaldrive current based on the resonant actuator electrical output.

The invention includes a method of making a helicopter vibrationcanceling system for canceling vibrations generated in a helicopter. Themethod includes providing a resonant actuator 24 having a naturalresonant frequency, providing a resonant actuator electronic controlsystem 34 for providing an electrical drive current to drive theresonant actuator, and connecting the resonant actuator with theresonant actuator electronic control system wherein the resonantactuator electronic control system electrical drive current drives theresonant actuator about the natural resonant frequency, with theresonant actuator feeding an electrical output 44 back into the resonantactuator electronic control system wherein the resonant actuatorelectronic control system adjusts the electrical drive current based onthe resonant actuator electrical output. Providing resonant actuator 24preferably includes providing an electromagnetically driven voice coil,preferably a sprung mass 26 driven by modulating a electromagnetic fieldproduced by an EM coil 30 so the sprung mass is attracted and repelledby the EM field and the actuator resonates at its natural resonantfrequency. Providing the resonant actuator electronic control system 34preferably includes providing a resonant actuator electronic controlsystem having a command input 36 for receiving a command signal 38 and apower amplifier 40 for providing an electrical drive current (i) todrive the resonant actuator about its resonant frequency. Preferably thecommand signal 38 is an analog input voltage, with the analog variablevoltage input command signal commanding the control system to produce avibration canceling force 22 which destructively interferes with andcancels an unwanted vibration force in the structure 50 that theactuator 24 is attached to. In a preferred embodiment such as shown inFIG. 1, the actuator electrical output 44 is fed back directly into thecontrol system, preferably with no separate physical actuator motionsensor needed for producing the feedback output. In an alternativeembodiment, such as shown in FIG. 4, the resonant actuator electricaloutput 44 includes an actuator sensor electrical output from an actuatorsensor 54. The actuator sensor 54 provides an actuator sensor electricaloutput 44 relative to a physical motion characteristic of the actuator24, such as a motion sensor measuring the motion of the moving mass 26.In an embodiment the actuator sensor 54 is an accelerometer mounted onthe actuator driven sprung mass. In an embodiment the actuator sensor 54is a velocity sensor measuring and sensing the velocity of the actuatordriven sprung mass. In an embodiment the actuator sensor 54 is adisplacement sensor measuring and sensing the displacement and positionof the actuator driven sprung mass. Providing the resonant actuator 24,preferably includes providing a resonant actuator with a naturalresonant frequency in the range of 15 to 40 Hz, more preferably 15-30Hz, and most preferably 18 to 26 Hz. Providing the resonant actuator 24,preferably includes providing a resonant actuator which has a dampinglevel less than four percent of critical damping, more preferably lessthan two percent of critical damping. Preferably the actuator 24 is alightly damped resonant actuator with an effective damping ratio lessthan 0.5 (damping ratio=particular damping coefficient c/criticaldamping coefficient c_(r)). Preferably the actuator 24 has the highlyresonant response of a lightly damped mass spring system. In anembodiment the method includes providing an electrical connectorinterface 52 for disengagably connecting the resonant actuator 24 to theresonant actuator electronic control system 34, preferably including afeedback output loop connectors 52, and electrical drive currentconnectors 52, with the disengagement and engagement of the connectorinterfaces used to interchange of actuators 24 with the control system34, and for replacing and swapping out actuators 24 driven by thecontrol system 34. Feeding back the electrical feedback 44 preferablyincludes feeding back the electrical charge flow rate through theresonant actuator. The current (i) through the actuator 24 is fed backinto the control system as (i_act) with the drive current controlled andlimited to a maximum operation value, most preferably with no shapefiltering used to drive the actuator 24. In an embodiment of theinvention feeding back the electrical feedback 44 preferably includesfeeding back the electrical potential difference through the resonantactuator. The voltage across the actuator fed back into the controlsystem as (v_act), with the voltage is controlled and limited to amaximum value corresponding to the rated voltage for the actuator 24 formaximum operation displacement of the actuator at resonance. In anembodiment feeding back the electrical feedback 44 preferably includesfeeding back both the electrical charge flow rate through the resonantactuator and the electrical potential difference through the resonantactuator, with both the voltage and current feedback from actuator.

The invention includes a method of controlling helicopter vibrations.The method includes providing a resonant actuator having a naturalresonant frequency. The method includes mounting the resonant actuatorin a helicopter. The method includes providing a resonant actuatorelectronic control system for providing an electrical drive current todrive the resonant actuator. The method includes connecting the resonantactuator with the resonant actuator electronic control system. Themethod includes driving the resonant actuator about the natural resonantfrequency with the resonant actuator feeding an electrical output backinto the resonant actuator electronic control system and adjusting theelectrical drive current based on the resonant actuator electricaloutput.

The invention includes a method of controlling helicopter vibrations.The method includes providing a resonant actuator 24 having a naturalresonant frequency, mounting the resonant actuator in a helicopter to avibrating structure 50 of the helicopter, providing a resonant actuatorelectronic control system 34 for providing an electrical drive currentto drive the resonant actuator, connecting the resonant actuator withthe resonant actuator electronic control system, and driving theresonant actuator about the natural resonant frequency with the resonantactuator feeding an electrical output back into the resonant actuatorelectronic control system and adjusting the electrical drive currentbased on the resonant actuator electrical output. The method includesdriving the resonant actuator about the natural resonant frequency withthe resonant actuator feeding an electrical output back into theresonant actuator electronic control system and adjusting the electricaldrive current based on the resonant actuator electrical output.Preferably providing a resonant actuator 24 includes providing aresonant actuator with a natural resonant frequency in a range of 15 to40 Hz, more preferably 15-30 Hz, and most preferably 18 to 26 Hz.Preferably providing a resonant actuator 24 includes providing aresonant actuator with a damping level less than four percent ofcritical damping, more preferably less than two percent of criticaldamping. Preferably the lightly damped resonant actuator 24 has aneffective damping ratio less than 0.5 (damping ratio=particular dampingcoefficient c/critical damping coefficient c_(r)), with the actuatorhaving the highly resonant response of a lightly damped mass springsystem. Preferably the method includes providing an electrical connectorinterface 52 for disengagably connecting the resonant actuator to theresonant actuator electronic control system. Preferably the resonantactuator electrical output 44 is an electrical potential differencethrough the resonant actuator with the voltage across the actuator fedback into the control system, with voltage controlled/limited to amaximum value corresponding to the rated voltage for the actuator formaximum operation displacement of the actuator at resonance. Preferablythe resonant actuator electrical output 44 is an electrical charge flowrate through the resonant actuator. Preferably the resonant actuatorelectrical output is an electrical charge flow rate through the resonantactuator and an electrical potential difference through the resonantactuator. In an embodiment the resonant actuator electrical output is anactuator sensor electrical output.

The invention utilizes tuning of the current loop of the amplifier toprovide force shaping without using a shaping filter, with such tuninglimiting the maximum current and power delivered to the actuator atfrequencies away from resonance and, keeps the moving mass displacementsbelow fatigue limits at resonance. The amplifier behaves like a voltagecontrolled amplifier close to the resonance frequency and a currentcontrolled amplifier away from resonance. Since the actuator voltage isproportional to flexure displacement near resonance, limiting theactuator voltage near resonance protects the actuator from beingoverdriven. Preferably the magnitude of the trans-conductance dip of theamplifier is tuned to limit displacement at resonance and the pass-bandgain of the amplifier in order to limit the current/power away from theresonance frequency. The invention allows the system to adapt to changesin the resonance frequency. With the invention no data is required fromthe installed actuators and no shaping filters are required in thesystem. With the invention the actuators can be changed, swapped,repaired, and/or replaced without making any changes and/or adjustmentsto the electronic control system.

FIG. 6 shows a schematic of the vibration control actuator system. Theactuator system can be modeled using the following equations:

${{m\frac{\partial^{2}x}{\partial t^{2}}} + {c\frac{\partial x}{\partial t}}} = {{kx} = {F_{a}(t)}}$${{L\frac{i}{t}} + {Ri} + {\alpha \frac{\partial x}{\partial t}}} = v_{in}$F_(a)(t) = −α i$X = {\frac{\left( \frac{\alpha}{{Ls} + R} \right)}{\left( {{m\; s^{2}} + {cs} + {k\frac{\alpha^{2}s}{{Ls} + R}}} \right)}V_{in}}$$I = {\frac{1}{\left( {{Ls} + R + \frac{\alpha^{2}s}{{m\; s^{2}} + {cs} + k}} \right)}V_{in}}$

FIG. 7 shows the schematic of a current loop of the LUICU. The fivegains (g₁ through g₅) shown in the schematic are preferably optimized toachieve a desired performance. Preferably with loop optimization, thereare five parameters for optimization in the control scheme:

Input gain g₁Compensator gains g₂, g₃, g₄Feedback loop gain g₅Preferably with loop optimization, there are two considerations:

-   -   1) The system should not exceed the physical limits;    -   2) The system should have sufficient stability margins.        Preferably these gains are designed through a coupled        optimization study and a stability analysis, a number of cost        functions can be used for optimization and they will result in        different solutions, with examples and their comparison        presented here:

${\Phi \; 1} = {\left( \frac{{I\left( \omega_{1} \right)} - I_{\max}}{w\; 1} \right)^{2} + \left( \frac{{F\left( \omega_{n} \right)} - F_{req}}{w\; 2} \right)^{2}}$${\Phi \; 2} = {\left( \frac{{I\left( \omega_{1} \right)} - I_{\max}}{w\; 1} \right)^{2} + \left( \frac{{F\left( \omega_{n} \right)} - F_{req}}{w\; 2} \right)^{2} + \left( \frac{{P\left( \omega_{n} \right)} - P_{\max}}{w\; 3} \right)}$${\Phi \; 3} = {\left( \frac{{I\left( \omega_{1} \right)} - I_{\max}}{w\; 1} \right)^{2} + \left( \frac{{F\left( \omega_{n} \right)} - F_{req}}{w\; 2} \right)^{2} + \left( \frac{{P\left( \omega_{n} \right)} - P_{\max}}{\; {w\; 3}\;} \right)^{2}}$

where I_(max) and P_(max) are the maximum allowed current and powerrespectively. The F_(req) is the desired force.For simplicity and demonstration purposes, two gains are optimized, g₁and g₅, with the following values used:

-   -   I_(max)=5 amps, P_(max)=100 watts and F_(req)=3000 N    -   w1=300, w2=1 and w3=6    -   Φ₁₌₁₀ Hz, Φ_(n)=21.6 Hz        The below table shows the optimized gains for the three cost        functions. The system is optimized for 13 Kg moving mass

Cost Function g₁ g₅ Φ₁ 0.95555 0.10654 Φ₁ 1.0396 0.2585 Φ₁ 0.968870.13062The plots of FIG. 8-17 show the performance of the method/system. Inimplementation and lab testing the loop changes were implemented in theLCICU amplifier card and the system was tested. For testing, thefollowing values were used:

-   -   g1=0.295, g2=50, g3=2*pi*2.4, g4=2*pi*354, g5=0.1245; the        testing was done for an actuator mass of 14.2 and resonance of        21.72; the optimization was done for mass of 13; the test        demonstrated that the system performance was within specs. It is        noted that the mass estimation is important to limit the force,        since we tuned the resonant acceleration and not the force.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the invention withoutdeparting from the spirit and scope of the invention. Thus, it isintended that the invention cover the modifications and variations ofthis invention provided they come within the scope of the appendedclaims and their equivalents. It is intended that the scope of differingterms or phrases in the claims may be fulfilled by the same or differentstructure(s) or step(s).

1. An aircraft vibration canceling force generator for activelygenerating an aircraft vibration canceling force, said aircraftvibration canceling force generator comprising: an aircraft resonantactuator, said resonant actuator including an electromagnetically drivensprung mass, said resonant actuator having a resonant frequency, and aresonant actuator electronic control system having an input forreceiving a signal, said resonant actuator electronic control systemproviding an electrical drive current to said resonant actuator to drivesaid resonant actuator about said resonant frequency when commanded by areceived signal, said resonant actuator having a direct feedbackelectrical output, said direct feedback electrical output directly fedback into said resonant actuator electronic control system wherein saidresonant actuator electronic control system adjusts said electricaldrive current based on said resonant actuator direct feedback electricaloutput to generate said aircraft vibration canceling force.
 2. Anaircraft vibration canceling force generator as claimed in claim 1wherein said resonant actuator electromagnetically driven sprung mass issuspended on a stack of resilient flexures.
 3. An aircraft vibrationcanceling force generator as claimed in claim 2 wherein said stack ofresilient flexures is comprised of a horizontal beam stack of multiplelayers of resilient metal flexures.
 4. An aircraft vibration cancelingforce generator as claimed in claim 2 wherein said stack of resilientflexures is comprised of a plurality of metal flexures.
 5. An aircraftvibration canceling force generator as claimed in claim 1 wherein saidresonant actuator electromagnetically driven sprung mass is supported bya plurality of vertical side resilient flexure posts.
 6. An aircraftvibration canceling force generator as claimed in claim 2 wherein saidstack of resilient flexures is supported by a plurality of vertical sideresilient flexure post plates.
 7. An aircraft vibration canceling forcegenerator as claimed in claim 5 wherein said vertical side resilientflexure posts are resilient metal flexure post plates.
 8. An aircraftvibration canceling force generator as claimed in claim 1 including anelectrical connector interface for disengagably connecting said resonantactuator to said resonant actuator electronic control system.
 9. Anaircraft vibration canceling force generator as claimed in claim 1,wherein said resonant actuator direct feedback electrical output is anelectrical potential difference through said resonant actuator.
 10. Anaircraft vibration canceling force generator as claimed in claim 1,wherein said resonant actuator direct feedback electrical output is anelectrical charge flow rate through said resonant actuator.
 11. Anaircraft vibration canceling force generator as claimed in claim 1,wherein said resonant actuator direct feedback electrical output is anelectrical charge flow rate through said resonant actuator and anelectrical potential difference through said resonant actuator.
 12. Anaircraft vibration canceling force generator as claimed in claim 1,wherein said resonant actuator does not include a separate physicalactuator motion sensor.
 13. A method of making an aircraft vibrationcanceling force generator, said method comprising the steps of:providing an aircraft resonant actuator having a resonant frequency andan electrical output, providing a resonant actuator electronic controlsystem having an input for receiving a signal, said electronic controlsystem providing an electrical drive current to drive said resonantactuator, connecting said resonant actuator with said resonant actuatorelectronic control system wherein said resonant actuator electroniccontrol system electrical drive current drives said resonant actuatorabout said resonant frequency when commanded by a received signal, withsaid resonant actuator feeding said electrical output back into saidresonant actuator electronic control system wherein said resonantactuator electronic control system adjusts said electrical drive currentbased on said resonant actuator electrical output.
 14. A method asclaimed in claim 13 wherein providing a resonant actuator includesproviding a resonant actuator with an electromagnetically driven sprungmass.
 15. A method as claimed in claim 14 wherein said resonant actuatorelectromagnetically driven sprung mass is suspended on a stack ofresilient flexures.
 16. A method as claimed in claim 13 wherein saidmethod includes providing an electrical connector interface fordisengagably connecting said resonant actuator to said resonant actuatorelectronic control system.
 17. A method as claimed in claim 13, whereinsaid resonant actuator electrical output is an electrical potentialdifference through said resonant actuator.
 18. A method as claimed inclaim 13, wherein said resonant actuator electrical output is anelectrical charge flow rate through said resonant actuator.
 19. A methodas claimed in claim 13, wherein said resonant actuator electrical outputis an electrical charge flow rate through said resonant actuator and anelectrical potential difference through said resonant actuator.
 20. Amethod as claimed in claim 13 wherein providing a resonant actuatorincludes providing a resonant actuator said resonant actuator that doesnot include a separate physical actuator motion sensor.
 21. A method ofcontrolling aircraft vibrations, said method comprising the steps of:providing a resonant actuator, said resonant actuator including anelectromagnetically driven sprung mass, said resonant actuator having aresonant frequency and an electrical output, providing an electroniccontrol system for providing an electrical drive current to drive saidresonant actuator, connecting said resonant actuator with saidelectronic control system, electromagnetically driving said resonantactuator about said resonant frequency with said resonant actuatorfeeding said electrical output back into said electronic control systemand adjusting said electrical drive current based on said resonantactuator electrical output.
 22. A method as claimed in claim 21 whereinsaid resonant actuator electromagnetically driven sprung mass issuspended on a stack of resilient flexures.
 23. A method as claimed inclaim 21 wherein said resonant actuator electromagnetically drivensprung mass is supported by a plurality of vertical side resilientflexure posts.
 24. A method as claimed in claim 21 wherein said methodincludes providing an electrical connector interface for disengagablyconnecting said resonant actuator to said electronic control system. 25.A method as claimed in claim 21, wherein said resonant actuatorelectrical output is an electrical potential difference through saidresonant actuator.
 26. A method as claimed in claim 21, wherein saidresonant actuator electrical output is an electrical charge flow ratethrough said resonant actuator.
 27. A method as claimed in claim 21,wherein said resonant actuator electrical output is an electrical chargeflow rate through said resonant actuator and an electrical potentialdifference through said resonant actuator.
 28. A method as claimed inclaim 21, wherein said resonant actuator electrical output is not from aseparate physical actuator motion sensor.
 29. A method as claimed inclaim 21, wherein said electronic control system includes an amplifierwith a current loop, and the method includes controlling said amplifieras a voltage controlled amplifier proximate said resonant frequency andcontrolling said amplifier as a current controlled amplifier away fromsaid resonant frequency.
 30. A helicopter, said helicopter havinghelicopter vibrations, said helicopter including a helicopter vibrationcanceling system, said vibration canceling system comprising at leastone resonant actuator, said resonant actuator including anelectromagnetically driven sprung mass, said resonant actuator having aresonant frequency, and a resonant actuator electronic controller, saidresonant actuator electronic controller providing an electrical drivecurrent to said resonant actuator to electromagnetically drive saidresonant actuator about said resonant frequency, said resonant actuatorhaving a feedback electrical output, said feedback electrical output fedback into said resonant actuator electronic controller wherein saidresonant actuator electronic controller adjusts said electrical drivecurrent based on said resonant actuator feedback electrical output withsaid helicopter vibration canceling system controlling said helicoptervibrations.
 31. A helicopter as claimed in claim 30 wherein saidresonant actuator electromagnetically driven sprung mass is suspended ona stack of resilient flexures.
 32. A helicopter as claimed in claim 31wherein said stack of resilient flexures is comprised of a horizontalbeam stack of multiple layers of resilient metal flexures.
 33. Ahelicopter as claimed in claim 31 wherein said stack of resilientflexures is comprised of a plurality of metal flexures.
 34. A helicopteras claimed in claim 30 wherein said resonant actuatorelectromagnetically driven sprung mass is supported by a plurality ofvertical side resilient flexure posts.
 35. A helicopter as claimed inclaim 31 wherein said stack of resilient flexures is supported by aplurality of vertical side resilient flexure post plates.
 36. Ahelicopter as claimed in claim 34 wherein said vertical side resilientflexure posts are resilient metal flexure post plates.
 37. A helicopteras claimed in claim 30 including an electrical connector interface fordisengagably connecting said resonant actuator to said resonant actuatorelectronic control system.
 38. A helicopter as claimed in claim 30wherein said resonant actuator feedback electrical output is anelectrical potential difference through said resonant actuator.
 39. Ahelicopter as claimed in claim 30 wherein said resonant actuatorfeedback electrical output is an electrical charge flow rate throughsaid resonant actuator.
 40. A helicopter as claimed in claim 30 whereinsaid resonant actuator feedback electrical output is an electricalcharge flow rate through said resonant actuator and an electricalpotential difference through said resonant actuator.
 41. A helicopter asclaimed in claim 30 wherein said resonant actuator does not include aseparate physical actuator motion sensor.